Tonneau/half tonneau.....spoiler/half template

[hat_man]

My MS Paint skills are rather laking aren't they?

I agree with the "solid object" idea but there is a low pressure zone created just behind the cab. I have a full soft tonneau now and can see the pressure difference as the soft cover is lifted behind the cab and pressed down at the rear.

[kach22i]

Originally Posted by hat_man

Here are some really bad diagrams of what I am getting at and the red/yellow options.

I'm thinking Hat-Man's questions are academic and not a literal design proposal, yes?

I would do either the yellow line level cover or the red line level but not both at the same time.

The higher one (yellow) will probably create the larger bubble of air for the other air traveling over the cab to flow over. This is a good thing if it's closest to the Aero-Template. The template is "everything" because it considers the ground pressure plane, a complexity I struggle with at a conceptual level but think I understand a little bit.

The Ridgeline inspired side sails should cant/angle inward about 10 degrees to be most effective.

If you can get a partial roof wing incorporated into it, all the better, that too shall have a cant/angle downward 10 degrees.

[hat_man]

Katch22i you've hit the nail on the head. It is more academic than design. I wouldn't do both levels (red and yellow) at the same time but wasn't sure how to show the different options until the really bad paint diagrams. I was under the same impression that having a larger volume of trapped air would create a slightly lower pressure (higher pressure differential) across the tailgate, but had no clue if my assumptions were correct.

I believe the Ridgeline side rails do cant inward but I don't have a clue at what angle.

So if my hypothetical vehicle did exist having the Ridgeline sail panels and the sloped and canted side rails with the yellow cover would be the more beneficial option, right? It's too bad Honda didn't think of it, but from a selling point of view it probably wouldn't go over anyhow. If they had turned the roll up bed cover around 180° you could almost use it as a half tonneau if it would lock in place there. Or even had the roll up bed cover follow the sloped bed rails. It would have created a larger storage compartment and allowed for at least a downward sloping surface (albeit well below the template) for air coming over the cab to move along. Turning the roll up bed cover 180° and having it lock in place at the halfway point and following the sloped rails might have worked a little better yet.

[kach22i]

Originally Posted by hat_man

......I was under the same impression that having a larger volume of trapped air would create a slightly lower pressure (higher pressure differential) across the tailgate, but had no clue if my assumptions were correct.

I believe the Ridgeline side rails do cant inward but I don't have a clue at what angle...........

Forget about larger or smaller volumes, does it fill out the template or not!!!!

On my S10 the rear spoiler works because it fills out the template. You can be a little higher or a little lower, point is to get as close as possible. The Bonneville racers tend to go in the horizontal direction in lieu of my 45 degree spoiler but the concept is similar - fill out the bloody template mate.

aero bed cap questions
https://ecomodder.com/forum/showthre...ons-35060.html


The 10-degree surface rule is a safe bet for air attachment.

Some conditions warrant greater or lesser angles, again it all goes back to the Aero-Template.

May the template guide you in your journey.

Aerodynamic streamline template - online tool (view streamlined extension on any car)
https://ecomodder.com/forum/showthre...n-21952-2.html


Aerodynamic Streamlining Template: Part-C
https://ecomodder.com/forum/showthre...tml#post116392


EDIT:

You might want to read Aerohead's post #4 in the link below for a more informed opinion.

Tonneau cover extension/spoiler
https://ecomodder.com/forum/showthre...ler-27829.html




EDIT-2:

My rear spoiler used to be adjustable - I forgot about that, it rusted to it's current angle years ago.

http://forums.pelicanparts.com/off-t...eriment-2.html


EDIT-3:

From a 2012 hat_man started thread........................

Pickup bed aerodynamics idea. Any thoughts?
https://ecomodder.com/forum/showthre...hts-22378.html

[hat_man]

I'm not trying to argue so please don't take offense, but I'm not trying to fill out the template. Like I said, we all know that the template is the Holy Grail but that's not what I'm after. What I am trying to learn about is relating to this from Aerohead:

Originally Posted by aerohead

*Without the tonneau cover,there's nothing but turbulence back there.All the kinetic energy is lost forever,and there's no chance for any re-attachment.A lot of drag and a lot of lift.
*The tonneau provides a surface of re-attachment for the separated flow,allowing for a much smaller wake,and it kills most of the rear lift.
*The half-tonneau is a peculiar animal.It allows a locked-vortex to be captured behind the rearward facing step of the cab.
*The inviscid (streamline flow) follows over the vortex as if it were more a solid body,strikes the tail end's upper surface,really killing lift.
*The extremely low pressure of the 'eye' of the vortex is transferred to the inner face of the tailgate.This inner face is at a lower pressure than behind the gate,creating a pressure differential which 'pushes' the gate forwards,something which doesn't happen with a full tonneau.....

What I was curious about was how the "extremely low pressure eye of the vortex" being transferred to the inner face of the tailgate is affected by the size of the area (volume) of the space under the cover.

Let's throw some numbers at it. If I cover the back half of a 6' bed of a Ranger it makes a covered area of about 19 sq. ft. that is open to the front portion of the bed. Air moving at 55 mph over the cab creates a low pressure vortex behind the cab that is transferred to the inner face of the tail gate. Let's quantify this pressure as (X). This would be like the red cover without the Ridgeline rails.

If the Ridgeline rails were added and the red cover was used again at the same 55 mph, the only difference I can see is that some of the air flow over the cab might be slightly "captured" and better directed over the half cover rather than being allowed to freely spill outwards like it would with the red cover and NO rails. Unless (?) the air flowing down the sides of the truck (doors and bedsides) creates a barrier that keeps the air flowing over the cab from spilling outwards. That I don't know. The question in this instance is....Is this new pressure (Y) with the red cover and Ridgeline rails greater than/less than/or equal to pressure (X) with the red cover and no rails? I'm thinking maybe greater than, but only very slightly.

The other question would concern the yellow cover. If you added the Ridgeline rails to a Ranger and used the yellow cover (on top of the Ridgeline rails which are slightly sloped) it would create an area of about 24 sq. ft. under the cover yet still open to the front portion of the bed. Nearly 5 sq. ft. larger than the red cover area. So the same 55 mph now creates a low pressure vortex behind the cab that interacts with a larger volume of air to create a new pressure at the tailgate we could call (Z) Given the same low pressure vortex and the new larger volume of air, is (Z) greater than/less than/or equal to (X)?

I wasn't worried about filling out the template so much, and maybe it was a little misleading me mentioning it in relation to the Ridgeline rails. In my mind I was seeing the sloped rails creating a sloped cover that might be more beneficial than the flat red cover on the plain Ranger bed.

[freebeard]

I'm not trying to argue so please don't take offense....

Argument is merely contradiction (Monty Python). Then you have debate and dialectic. This is one of those.

Originally Posted by hat_man

Originally Posted by myself

Do you know those cylindrical hay bales? Imagine one the width of the bed and 80% the height of the cab, ahead of the half tonneau, and spinning. I think the half tonneau creates a vortex that acts like a solid object in that space.

I tried.

Insofar as the sail panels, they will likely promote inward rolling vortexes over the tonneau, which would reattach. Against the main vortex, who knows. Build and tuft test it. The shape of the top rear edge of the cab may be more significant.

And I wonder about the front face of the tailgate. If the half-tonneau is a box with a front wall, won't the low pressure tramsit through the rigid structure of the bed? And how does the low pressure at the center get through the spinning mass of air?

[hat_man]

Originally Posted by freebeard

And I wonder about the front face of the tailgate. If the half-tonneau is a box with a front wall, won't the low pressure tramsit through the rigid structure of the bed? And how does the low pressure at the center get through the spinning mass of air?

That's a question that I can't answer. I was only going by what Aerohead had said and I hoped I had interpreted correctly.

This air flow picture may have answered my question about the flow spilling outwards after the cab, but I can't confirm it. I'm not quite that smart.

The other picture is the one we have seen many times. I currently have the full bed cover and get about 32 mpg in my logs. I am aiming for the cab wing and half cover (towards the bottom of the picture) someday. The half cover is an easy project and I thought it might be interesting to see how it performs without the wing. I'm more than willing to build it and find out. If it's an improvement over the 32mpg, then I'll keep it. If it's not then I'll try and figure out the cab wing and record how that does combined with the half cover. I'm sure it will be an improvement if the picture is correct (and I'm sure it is). Hucho doesn't show a wing and full cover combination (harder for me to fabricate the wing) or the half cover and no wing (much easier for me to fabricate). The way I want to design the half cover, will allow me to someday test the wing and full cover theory also. That is if I can figure out the wing assembly.

[hat_man]

I wonder how this would work in combination with a half bed cover?

[kach22i]

Originally Posted by hat_man

I wonder how this would work in combination with a half bed cover?

That's apparently a still from a video.

https://www.youtube.com/watch?v=nmZdPy1wqBg

Let's see, the partial aero-cap covers 1/3 of the bed, the partial cover occupies the latter 1/3, so 1/3 is open in the middle.

It would be a dead zone of some sort that the air overhead would skip over.

I never took anything hat_man said as negative, just at times I think he's wringing the towel a bit too much and should just hang it on the line to dry.

[freebeard]

I wouldn't trust that first picture, since tailgate up is (empirically) better than tailgate down. And I don't see how the cab wing helps the half-tonneau. But there you go.

More to mull over:



The manager of the pizza parlor knew this gets better gas mileage (around town) but didn't know how much. It's basically a lockable trunk and spoiler combo. I think the ends could be beveled at 45° or rounded.